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For further information, see CMDT Part 7-09: Infectious Keratitis

Key Features

  • Important categories of infectious keratitis include: bacterial, herpetic, fungal, and amebic

  • Bacterial keratitis

    • Risk factors

      • Contact lens wear—especially overnight wear

      • Corneal trauma, including refractive surgery

    • Commonly isolated pathogens

      • Staphylococci, including methicillin-resistant Staphylococcus aureus (MRSA)

      • Streptococci

      • Pseudomonas aeruginosa

      • Moraxella species

      • Other gram-negative bacilli

  • Herpes simplex keratitis

    • An important cause of ocular morbidity

    • The ability of the virus to colonize the trigeminal ganglion leads to recurrences that may be precipitated by fever, excessive exposure to sunlight, or immunodeficiency

    • Herpetic corneal disease is typically unilateral but can occur bilaterally in the setting of atopy or immunocompromise

  • Herpes zoster ophthalmicus

    • Frequently involves the ophthalmic division of the trigeminal nerve

    • Long-term complications

      • Recurrent anterior segment inflammation

      • Neurotrophic keratitis

      • Posterior subcapsular cataract

    • Optic neuropathy, cranial nerve palsies, acute retinal necrosis, and cerebral angiitis occur infrequently

    • HIV infection is an important risk factor and increases the likelihood of complications

  • Fungal keratitis

    • Tends to occur after corneal injury involving plant material or in an agricultural setting, in eyes with chronic ocular surface disease, and in contact lens wearers

    • Usually an indolent process

  • Amoebic keratitis

    • Seen in contact lens wearers

    • Severe pain with perineural and ring infiltrates in the corneal stroma

Clinical Findings

  • Bacterial keratitis

    • Cornea has an epithelial defect and an underlying opacity

    • Hypopyon may be present

  • Herpes simplex keratitis

    • The dendritic (branching) corneal ulcer is the most characteristic manifestation of herpetic corneal disease

    • More extensive ("geographic") ulcers also occur, particularly if topical corticosteroids have been used

    • Stromal herpes simplex keratitis produces increasingly severe corneal opacity with each recurrence

  • Herpes zoster ophthalmicus

    • Malaise, fever, headache, and periorbital burning and itching may precede the eruption by a day or more

    • The rash is initially vesicular, quickly becoming pustular and then crusting

    • Involvement of the tip of the nose or the lid margins predicts involvement of the eye

    • Ocular signs include conjunctivitis, keratitis, episcleritis, and anterior uveitis, often with elevated intraocular pressure

  • Fungal keratitis

    • May be an indolent process

    • Corneal infiltrate may have feathery edges and multiple “satellite” lesions

    • A hypopyon may be present

    • Unlike bacterial keratitis, an epithelial defect may or may not be present

  • Amoebic keratitis

    • Although severe pain with perineural and ring infiltrates in the corneal stroma is characteristic, earlier forms are identifiable with changes confined to the corneal epithelium

Diagnosis

  • Bacterial keratitis

    • For severe central ulcers, diagnostic scrapings can be sent for Gram stain and culture

  • Herpes simplex keratitis

    • These ulcers are most easily seen after instillation of fluorescein and examination with a blue light

  • Herpes zoster ophthalmicus

    • Diagnosis usually made on clinical grounds alone

    • Direct fluorescent antibody staining of exudate from the base of any unroofed lesion among the grouped, tense, deep-seated vesicles is diagnostic

  • Fungal keratitis

    • Corneal scrapings should be cultured on media suitable for fungi

    • Diagnosis is often delayed

  • Amoebic keratitis

    • Diagnosis is facilitated by confocal microscopy and ...

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